I just thought I'd add an accompaniment to the beginners water treatment post (
here) for anyone who fancies a little more fine tuning. This step isn't necessary but once you have a grasp on the basics of water treatment, you may want to advance to this step for a little more control over your brew.
Sulphate:Chloride Ratio
As mentioned in the OP, sulphate and chloride are ions which can be manipulated to enhance certain characteristics of a beer (see exbeeriment
here). It seems to be the case that the ratio between these two ions is more important than the overall concentration of them in determining which flavours are enhanced. In other words, water with 100ppm sulphate and 50ppm chloride will be effectively the same as water with 250ppm sulphate and 125ppm chloride because they have the same ratio of 2:1 (or 2.0). (Brulosophy did an experiment backing this up
here.) For this effect however, a fairly moderate ion concentration is required. Aim for a minimum of 50ppm or so for both sulphate and chloride.
So we can use varying amounts of gypsum and/or calcium chloride to aim for the desired ratio. Now this should be done according to personal taste, but the following table should give you a good idea of where to start (
source):
0 - 0.4: Too Malty
0.4 - 0.6: Very Malty
0.6 - 0.8: Malty
0.8 - 1.5: Balanced
1.5 - 2.0: Slightly Bitter
2 - 4: Bitter
4 - 9: Very bitter
9+: Too bitter!
Obviously in order to do this, you will require knowledge of your water's concentration of sulphate and chloride which are usually included on the water report from your supplier. These figures will not be terribly accurate, but should be close enough for our purposes. You can now determine how much gypsum/calcium chloride to add to achieve the desired ratio. The following tables tell you the increase in sulphate or chloride when adding salts. I've also included increase in calcium just for reference.
Gypsum:
Addition - Increase in sulphate - Increase in calcium
0.1 g/L - 56 ppm - 23 ppm
0.2 g/L - 112 ppm - 46 ppm
0.3 g/L - 167 ppm - 69 ppm
0.4 g/L - 223 ppm - 92 ppm
0.5 g/L - 279 ppm - 115 ppm
0.6 g/L - 335 ppm - 138 ppm
Calcium Chloride:
Addition - Increase in chloride - Increase in calcium
0.1g/L - 48 ppm - 27 ppm
0.15g/L - 72 ppm - 41 ppm
0.2g/L - 97 ppm - 54 ppm
0.25g/L - 121 ppm - 68 ppm
0.3g/L - 145 ppm - 81 ppm
Examples:
Say you want to brew a red ale and your tap water has 140ppm sulphate and 50ppm chloride. Currently the ratio is 2.8 (140 divided by 50) which is ideal for an IPA but not for a red ale. Say you want to aim for a ratio of 0.8 which means increasing the chloride. As you can see above, adding 0.25g/L of calcium chloride will give you a ratio of 140:171 which is 0.82, pretty close. (Note you may need to add more salts depending on the calcium level of your tap water.)
If you use RO water then it's very simple. For example, if I was brewing a very bitter DIPA then I want to add around 100 ppm of calcium with a sulphate:chloride ratio of about 4:1. As you can see from the tables above, an addition of 0.4g/L of gypsum and 0.1g/L of calcium chloride will give me:
calcium - 119ppm
sulphate - 223ppm
chloride - 48ppm
Ratio of 4.6
Which is close enough.
Be aware however that it's not always possible to achieve the desired water profile, depending on your tap water's mineral content. In general it's best to keep sulphate levels below 400ppm, and considerably lower if the chloride is high, otherwise you could get a harsh, minerally flavour in your beer. Chloride should generally be kept below 150ppm, again especially important if the sulphate is high. In other words, you don't want both the sulphate and chloride to be at, or close to, their maximum. So in some cases it may be necessary to use low mineral bottled water such as Tesco Ashbeck, or to dilute your tap water with reverse osmosis (RO) water.
Any questions, please ask and I'll do my best to answer them.
For a more indepth article on water treatment see the excellent Water Knowledge page from Bru'n Water (
here).
